They are so useful !! In fact they're much more useful in their second life than as mere packaging for olives or jam. Personally I reuse them for my spices and pulses, keeps the bugs away ! Works for namkeen and biscuits as well, keeping them fresh & crispy for a long time :)
I also reused liquor bottles for my oil, almost every different liquor has it's own different bottle shape, so after thorough cleaning with vinegar, they make my oils look much better in the kitchen, and I can tell my olive oil apart from the cooking oil in the blink of an eye ;)
Also, trying to do my bit for the planet by just buying refills when I can, instead of buying oil in a plastic bottle each time.
I'm taking this occasion to urge you to visit this amazing website http://www.zerowastehome.com/. I keep checking it out for infinite ways to reduce waste. So inspiring!! she makes it all look so simple, I'm trying to get there step by step.